Pool Chemical Dosage: Chlorine, pH and Algaecide per Cubic Meter

Concentrations below 1.0 ppm result in inadequate disinfection, while levels above 3.0 ppm cause eye and skin irritation. In practice, keeping most pools at 1.5-2.0 ppm is enough.

In routine chlorination, raising free chlorine by 1.0 ppm in 10 m³ of water requires about 10 grams of available chlorine, which corresponds to roughly 18 grams of 56% sodium dichlor granules. For a 48 m³ pool, raising chlorine by 1 ppm therefore requires roughly 85 grams. These are typical calculation values: if your product has a different available chlorine content, the quantity changes and the product label takes precedence. During hot summer peaks, test water daily at sunset, once direct sunlight has passed.

Shock (superchlorination) raises chlorine to 5.0-10.0 ppm to eliminate chloramines, bacteria and algae spores. For a rapid-dissolving product with around 56% available chlorine, the typical shock range is 10-20 grams per m³; for other concentrations, follow the label. Shock is applied at dusk with continuous filtration overnight, because daytime UV breaks down most of the chlorine before it can work. Never swim until chlorine drops below 3.0 ppm.

The target range is strictly 7.2-7.6. Outside this band, chlorine efficacy drops sharply: at pH 8.0, chlorine loses over 50% of its sanitizing power. Dosing chlorine without balancing pH first is like carrying water in a perforated bucket.

When pH rises, pH Minus (sodium bisulfate or dilute acid) is dosed. As a baseline rule, lowering pH by 0.2 units in 10 m³ requires roughly 100-150 grams of pH Minus, depending on total alkalinity and product composition; the product label takes precedence. When pH is low, pH Plus (sodium carbonate) is added. Circulate water 4-6 hours before re-testing.

Total Alkalinity (TA) must be monitored alongside pH; the target range is 80-120 ppm. Alkalinity acts as the chemical buffer stabilizing pH: when TA is balanced, pH remains steady; when TA is low, pH fluctuates wildly. Stabilize alkalinity first to lock in pH.

Test results, water balance and disinfection are assessed together. A pH deviation changes how chlorine performs and can also affect how pool finishes and equipment surfaces behave. A chlorine reading alone therefore cannot guide every maintenance decision.

Once an active algae bloom establishes, algaecide alone cannot clear it; its function is inhibiting algae spores from germinating. Algaecide must be used as a routine weekly preventative.

Algaecide concentrations vary widely between products, so the following figures are a typical range and the label takes precedence. Standard preventative maintenance dosing is 3-5 ml of non-foaming algaecide per m³ weekly (approx. 150-250 ml weekly for a 48 m³ pool). A higher initial dose (8-10 ml/m³) is applied at spring opening. Dose algaecide with pumps running for uniform distribution.

Always specify non-foaming algaecides; foaming products leave persistent surface foam and a film on the water. Base the selection on the product label and safety data sheet.

Adding chemicals in the wrong sequence can neutralize active ingredients or produce dangerous chemical reactions. The correct protocol: first balance Total Alkalinity and pH; once water stabilizes, dose chlorine; and finally add algaecides or clarifiers.

Never mix different dry or concentrated liquid chemicals together. Always add each chemical separately directly into the pool over return jets with the pump running, allowing at least several hours between treatments.

Always add chemicals to water, never water to concentrated chemicals. Where the label recommends this method, dissolving granular products in a clean bucket of pool water prior to distribution prevents concentrated granules from settling onto and bleaching PVC liners or colored mosaic grout.

Do not combine acid, chlorine or different types of chlorine in the same container, and do not use the same measuring cup for them; even residues can react. Keep a separate, clean measuring cup for each product.

Do not work with a chemical whose label is unreadable or that has been transferred to another container. Store products in their original packaging, under the conditions stated by the manufacturer and out of reach of unauthorised people, especially children. Protection, storage and application conditions are set out in the product's safety data sheet.

While ideal CYA is 30-50 ppm to protect chlorine from sunlight UV breakdown, levels exceeding 80-100 ppm over-stabilize the water, binding chlorine and slowing disinfection considerably. Stabilized tablet users inadvertently build up CYA because stabilizer never evaporates.

Common pool chemicals cannot lower cyanuric acid; the reliable solution in practice is draining a portion of pool water and refilling with fresh water. Prevent chlorine lock by alternating stabilized tablets with unstabilized liquid chlorine and testing CYA monthly.

Always collect water samples at elbow depth (approx. 40 cm below surface) away from return jets and skimmer mouths; surface water does not reflect bulk water chemistry.

Chemical reagents degrade over time; replace test tablets and liquid reagents annually and store testing kits in a cool, dark cabinet. DPD photometers or liquid drop kits provide far greater precision than test strips for important balancing decisions.

Never test immediately after adding chemicals; allow 4-6 hours of continuous filtration for complete homogenization, although the time can vary with the system's turnover period and the product instructions. Testing prematurely leads to false readings and accidental double-dosing.

Record the product, quantity, time and pump status for every treatment. If the result differs from what you expected, check the test method, volume calculation and product concentration again before adding a second dose. Also check the test kit's measuring range and the reagents' expiry date; a total chlorine reading does not give the same information as a free chlorine reading.

Please also state which test method you used.

With this information, the problem usually turns out to be the measurement rather than a lack of product. It also shows whether routine maintenance or an on-site inspection is needed.